The incredibly hot, rocky planet, called Cancri e, has a mass eight times greater than our planet and orbits a sun-like star visible to the naked eye in the constellation of Cancer. It orbits at hyper speed, moving so fast that its years last only 18 hours.

In addition to diamond the planet appears to be composed of other forms of carbon, iron, silicon and carbide; in contrast to Earth, which is low in carbon. Its carbon-rich composition could influence the planet's thermal characteristics and plate tectonics, with implications for volcanoes, earthquakes and mountain formation.

The study, carried out by a US-French research team at the Institute de Recherche en Astrophysique et Planetologie in Toulouse, France, believes that a third of the planet's mass – the equivalent of about three Earth masses – could be diamond.

Nikku Madhusudhan, one of the lead researchers whose findings are due to be published in the journal Astrophysical Journal Letters, told Reuters, “The surface of this planet is likely covered in graphite and diamond rather than water and graphite.”

Diamond planets have been discovered before, but this is the first time one has been seen orbiting a sun-like star.

Madhusudhan explained that this was the first glimpse of a rocky world with a fundamentally different chemistry from Earth's. He added that the discovery of the carbon-rich planet means that distant rocky planets can no longer be assumed to be similar to Earth – namely to have atmospheres, interiors, chemical constituents or biologies like Earth.

David Spergel, an astronomer at Princeton University, explained that while it was quite simple to work out the basic history and structure of a star once you know its mass and age, planets were much more complex.

“This ‘diamond-rich super-Earth’ is likely just one example of the rich sets of discoveries that await us as we begin to explore planets around nearby stars,” he said.

But any fortune hunters will be thwarted by the distance involved in astronomy, as Cancri e is about 40 light years – or 230 trillion miles – from Earth.